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91-506: The Crossosomatales are an order, first recognized as such by APG II . They are flowering plants included within the Rosid eudicots . Species assigned to the Crossosomatales have in common flowers that are positioned solitarily, with the base of the calyx , corolla , and stamens fused into a tube-shaped floral cup , sepals overlapping, the outermost smaller than the inner. Insides of

182-500: A biochemical pump that collects carbon from the organ interior (or from the soil ) and not from the atmosphere. Cyanobacteria possess carboxysomes , which increase the concentration of CO 2 around RuBisCO to increase the rate of photosynthesis. An enzyme, carbonic anhydrase , located within the carboxysome, releases CO 2 from dissolved hydrocarbonate ions (HCO 3 ). Before the CO 2 can diffuse out, RuBisCO concentrated within

273-406: A clade, but the dicots were not, with a number of former dicots being placed in separate groups basal to both monocots and the remaining dicots, the eudicots or 'true dicots'. The overall scheme was relatively simple. This consisted of a grade consisting of isolated taxa (referred to as ANITA ), followed by the major angiosperm radiation , clades of monocots, magnolids and eudicots. The last being

364-425: A classification system have resulted from this collaboration, published in 1998, 2003, 2009 and 2016. An important motivation for the group was what they considered deficiencies in prior angiosperm classifications since they were not based on monophyletic groups (i.e., groups that include all the descendants of a common ancestor). APG publications are increasingly influential, with a number of major herbaria changing

455-464: A common ancestor). An ordinal classification of flowering plant families was proposed as a "reference tool of broad utility". The broad approach adopted to defining the limits of orders resulted in the recognition of 40 orders, compared to, for example, 232 in Takhtajan's 1997 classification . In 1998 only a handful of families had been adequately studied, but the primary aim was to obtain a consensus on

546-409: A different leaf anatomy from C 3 plants, and fix the CO 2 at night, when their stomata are open. CAM plants store the CO 2 mostly in the form of malic acid via carboxylation of phosphoenolpyruvate to oxaloacetate , which is then reduced to malate. Decarboxylation of malate during the day releases CO 2 inside the leaves, thus allowing carbon fixation to 3-phosphoglycerate by RuBisCO. CAM

637-474: A distinct group. At first there was a reluctance to develop a new system based entirely on a single gene. However, subsequent work continued to support these findings. These research studies involved an unprecedented collaboration between a very large number of scientists. Therefore, rather than naming all the individual contributors a decision was made to adopt the name Angiosperm Phylogeny Group classification, or APG for short. The first publication under this name

728-401: A large clade with smaller subclades and two main groupings, rosids and asterids , each in turn having two major subclades. As the overall relationship between groups of flowering plants became clearer, the focus shifted to the family level, in particular those families generally accepted as problematic. Again, consensus was achieved relatively easily resulting in an updated classification at

819-490: A larger group. The authors stated that they have generally accepted the views of specialists, although noting that specialists "nearly always favour splitting of groups" regarded as too varied in their morphology. APG II continued and indeed extends the use of alternative 'bracketed' taxa allowing the choice of either a large family or a number of smaller ones. For example, the large family Asparagaceae includes seven 'bracketed' families which can either be considered as part of

910-480: A phospholipid outer membrane, and an intermembrane space. Enclosed by the membrane is an aqueous fluid called the stroma. Embedded within the stroma are stacks of thylakoids (grana), which are the site of photosynthesis. The thylakoids appear as flattened disks. The thylakoid itself is enclosed by the thylakoid membrane, and within the enclosed volume is a lumen or thylakoid space. Embedded in the thylakoid membrane are integral and peripheral membrane protein complexes of

1001-479: A photocomplex. When a photon is absorbed by a chromophore, it is converted into a quasiparticle referred to as an exciton , which jumps from chromophore to chromophore towards the reaction center of the photocomplex, a collection of molecules that traps its energy in a chemical form accessible to the cell's metabolism. The exciton's wave properties enable it to cover a wider area and try out several possible paths simultaneously, allowing it to instantaneously "choose"

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1092-405: A photon by the antenna complex loosens an electron by a process called photoinduced charge separation . The antenna system is at the core of the chlorophyll molecule of the photosystem II reaction center. That loosened electron is taken up by the primary electron-acceptor molecule, pheophytin . As the electrons are shuttled through an electron transport chain (the so-called Z-scheme shown in

1183-422: A plant's photosynthetic response. Integrated chlorophyll fluorometer – gas exchange systems allow a more precise measure of photosynthetic response and mechanisms. While standard gas exchange photosynthesis systems can measure Ci, or substomatal CO 2 levels, the addition of integrated chlorophyll fluorescence measurements allows a more precise measurement of C C, the estimation of CO 2 concentration at

1274-450: A redox-active tyrosine residue that is oxidized by the energy of P680 . This resets the ability of P680 to absorb another photon and release another photo-dissociated electron. The oxidation of water is catalyzed in photosystem II by a redox-active structure that contains four manganese ions and a calcium ion ; this oxygen-evolving complex binds two water molecules and contains the four oxidizing equivalents that are used to drive

1365-399: A simpler method that employs a pigment similar to those used for vision in animals. The bacteriorhodopsin changes its configuration in response to sunlight, acting as a proton pump. This produces a proton gradient more directly, which is then converted to chemical energy. The process does not involve carbon dioxide fixation and does not release oxygen, and seems to have evolved separately from

1456-748: A smooth, woody coating. The relationships between orders within the Malvid clade, according to the APG system, is represented by the following tree. Geraniales Myrtales Crossosomatales Picramniales Sapindales Huerteales Brassicales Malvales Within the Crossosomatales, the APG III system of 2009 recognises families represented in the following tree. Strasburgeriaceae Geissolomataceae Aphloiaceae Staphyleaceae Guamatelaceae Stachyuraceae Crossosomataceae Angiosperm Phylogeny Group As of 2016 , four incremental versions of

1547-481: A source of carbon atoms to carry out photosynthesis; photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon. In plants, algae, and cyanobacteria, photosynthesis releases oxygen. This oxygenic photosynthesis is by far the most common type of photosynthesis used by living organisms. Some shade-loving plants (sciophytes) produce such low levels of oxygen during photosynthesis that they use all of it themselves instead of releasing it to

1638-534: A subsequent sequence of light-independent reactions called the Calvin cycle . In this process, atmospheric carbon dioxide is incorporated into already existing organic compounds, such as ribulose bisphosphate (RuBP). Using the ATP and NADPH produced by the light-dependent reactions, the resulting compounds are then reduced and removed to form further carbohydrates, such as glucose . In other bacteria, different mechanisms like

1729-405: A type of non- carbon-fixing anoxygenic photosynthesis, where the simpler photopigment retinal and its microbial rhodopsin derivatives are used to absorb green light and power proton pumps to directly synthesize adenosine triphosphate (ATP), the "energy currency" of cells. Such archaeal photosynthesis might have been the earliest form of photosynthesis that evolved on Earth, as far back as

1820-591: A wide variety of colors. These pigments are embedded in plants and algae in complexes called antenna proteins. In such proteins, the pigments are arranged to work together. Such a combination of proteins is also called a light-harvesting complex . Although all cells in the green parts of a plant have chloroplasts, the majority of those are found in specially adapted structures called leaves . Certain species adapted to conditions of strong sunlight and aridity , such as many Euphorbia and cactus species, have their main photosynthetic organs in their stems. The cells in

1911-626: Is a useful source for the latest research in angiosperm phylogeny which follows the APG approach. Other sources include the Angiosperm Phylogeny Poster and The Flowering Plants Handbook. a = listed as an author; c = listed as a contributor Photosynthesis Photosynthesis ( / ˌ f oʊ t ə ˈ s ɪ n θ ə s ɪ s / FOH -tə- SINTH -ə-sis ) is a system of biological processes by which photosynthetic organisms , such as most plants, algae , and cyanobacteria , convert light energy , typically from sunlight, into

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2002-490: Is an endothermic redox reaction. In general outline, photosynthesis is the opposite of cellular respiration : while photosynthesis is a process of reduction of carbon dioxide to carbohydrates, cellular respiration is the oxidation of carbohydrates or other nutrients to carbon dioxide. Nutrients used in cellular respiration include carbohydrates, amino acids and fatty acids. These nutrients are oxidized to produce carbon dioxide and water, and to release chemical energy to drive

2093-498: Is both an evolutionary precursor to C 4 and a useful carbon-concentrating mechanism in its own right. Xerophytes , such as cacti and most succulents , also use PEP carboxylase to capture carbon dioxide in a process called Crassulacean acid metabolism (CAM). In contrast to C 4 metabolism, which spatially separates the CO 2 fixation to PEP from the Calvin cycle, CAM temporally separates these two processes. CAM plants have

2184-474: Is commonly measured in μmols /( m / s ), parts per million, or volume per million; and H 2 O is commonly measured in mmols /(m /s) or in mbars . By measuring CO 2 assimilation , ΔH 2 O, leaf temperature, barometric pressure , leaf area, and photosynthetically active radiation (PAR), it becomes possible to estimate, "A" or carbon assimilation, "E" or transpiration , "gs" or stomatal conductance , and "Ci" or intracellular CO 2 . However, it

2275-430: Is converted to CO 2 by an oxalate oxidase enzyme, and the produced CO 2 can support the Calvin cycle reactions. Reactive hydrogen peroxide (H 2 O 2 ), the byproduct of oxalate oxidase reaction, can be neutralized by catalase . Alarm photosynthesis represents a photosynthetic variant to be added to the well-known C4 and CAM pathways. However, alarm photosynthesis, in contrast to these pathways, operates as

2366-419: Is freed from its locked position through a classic "hop". The movement of the electron towards the photo center is therefore covered in a series of conventional hops and quantum walks. Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old. More recent studies also suggest that photosynthesis may have begun about 3.4 billion years ago, though

2457-412: Is further excited by the light absorbed by that photosystem . The electron is then passed along a chain of electron acceptors to which it transfers some of its energy . The energy delivered to the electron acceptors is used to move hydrogen ions across the thylakoid membrane into the lumen . The electron is eventually used to reduce the coenzyme NADP with an H to NADPH (which has functions in

2548-451: Is more common to use chlorophyll fluorescence for plant stress measurement , where appropriate, because the most commonly used parameters FV/FM and Y(II) or F/FM' can be measured in a few seconds, allowing the investigation of larger plant populations. Gas exchange systems that offer control of CO 2 levels, above and below ambient , allow the common practice of measurement of A/Ci curves, at different CO 2 levels, to characterize

2639-406: Is passed through a food chain . The fixation or reduction of carbon dioxide is a process in which carbon dioxide combines with a five-carbon sugar , ribulose 1,5-bisphosphate , to yield two molecules of a three-carbon compound, glycerate 3-phosphate , also known as 3-phosphoglycerate. Glycerate 3-phosphate, in the presence of ATP and NADPH produced during the light-dependent stages,

2730-623: Is reduced to glyceraldehyde 3-phosphate . This product is also referred to as 3-phosphoglyceraldehyde (PGAL) or, more generically, as triose phosphate. Most (five out of six molecules) of the glyceraldehyde 3-phosphate produced are used to regenerate ribulose 1,5-bisphosphate so the process can continue. The triose phosphates not thus "recycled" often condense to form hexose phosphates, which ultimately yield sucrose , starch , and cellulose , as well as glucose and fructose . The sugars produced during carbon metabolism yield carbon skeletons that can be used for other metabolic reactions like

2821-459: Is significantly reduced. This requires the recognition of both new orders and new families compared to the previous classification. The number of orders goes up from 45 to 59; only 10 families are not placed in an order and only two of these ( Apodanthaceae and Cynomoriaceae ) are left entirely outside the classification. The authors say that they have tried to leave long-recognized families unchanged, while merging families with few genera. They "hope

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2912-429: Is then translocated to specialized bundle sheath cells where the enzyme RuBisCO and other Calvin cycle enzymes are located, and where CO 2 released by decarboxylation of the four-carbon acids is then fixed by RuBisCO activity to the three-carbon 3-phosphoglyceric acids . The physical separation of RuBisCO from the oxygen-generating light reactions reduces photorespiration and increases CO 2 fixation and, thus,

3003-404: Is then converted into the final carbohydrate products. The simple carbon sugars photosynthesis produces are then used to form other organic compounds , such as the building material cellulose , the precursors for lipid and amino acid biosynthesis, or as a fuel in cellular respiration . The latter occurs not only in plants but also in animals when the carbon and energy from plants

3094-499: Is used by 16,000 species of plants. Calcium-oxalate -accumulating plants, such as Amaranthus hybridus and Colobanthus quitensis , show a variation of photosynthesis where calcium oxalate crystals function as dynamic carbon pools , supplying carbon dioxide (CO 2 ) to photosynthetic cells when stomata are partially or totally closed. This process was named alarm photosynthesis . Under stress conditions (e.g., water deficit ), oxalate released from calcium oxalate crystals

3185-474: Is vital for climate processes, as it captures carbon dioxide from the air and binds it into plants, harvested produce and soil. Cereals alone are estimated to bind 3,825 Tg or 3.825 Pg of carbon dioxide every year, i.e. 3.825 billion metric tons. Most photosynthetic organisms are photoautotrophs , which means that they are able to synthesize food directly from carbon dioxide and water using energy from light. However, not all organisms use carbon dioxide as

3276-621: The Bentham & Hooker system in Britain (particularly influential because it was used by Kew ), the Takhtajan system in the former Soviet Union and countries within its sphere of influence and the Cronquist system in the United States. Before the availability of genetic evidence, the classification of angiosperms (also known as flowering plants , Angiospermae , Anthophyta or Magnoliophyta )

3367-572: The Paleoarchean , preceding that of cyanobacteria (see Purple Earth hypothesis ). While the details may differ between species , the process always begins when light energy is absorbed by the reaction centers , proteins that contain photosynthetic pigments or chromophores . In plants, these proteins are chlorophylls (a porphyrin derivative that absorbs the red and blue spectrums of light, thus reflecting green) held inside chloroplasts , abundant in leaf cells. In bacteria, they are embedded in

3458-408: The chemical energy necessary to fuel their metabolism . Photosynthesis usually refers to oxygenic photosynthesis , a process that produces oxygen. Photosynthetic organisms store the chemical energy so produced within intracellular organic compounds (compounds containing carbon) like sugars, glycogen , cellulose and starches . To use this stored chemical energy, an organism's cells metabolize

3549-637: The light reaction of photosynthesis by using chlorophyll fluorometers . Actual plants' photosynthetic efficiency varies with the frequency of the light being converted, light intensity , temperature , and proportion of carbon dioxide in the atmosphere , and can vary from 0.1% to 8%. By comparison, solar panels convert light into electric energy at an efficiency of approximately 6–20% for mass-produced panels, and above 40% in laboratory devices. Scientists are studying photosynthesis in hopes of developing plants with increased yield . The efficiency of both light and dark reactions can be measured, but

3640-434: The light-independent (or "dark") reactions, the enzyme RuBisCO captures CO 2 from the atmosphere and, in a process called the Calvin cycle , uses the newly formed NADPH and releases three-carbon sugars , which are later combined to form sucrose and starch . The overall equation for the light-independent reactions in green plants is Carbon fixation produces the three-carbon sugar intermediate , which

3731-417: The palisade mesophyll cells where most of the photosynthesis takes place. In the light-dependent reactions , one molecule of the pigment chlorophyll absorbs one photon and loses one electron . This electron is taken up by a modified form of chlorophyll called pheophytin , which passes the electron to a quinone molecule, starting the flow of electrons down an electron transport chain that leads to

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3822-417: The photosynthetic capacity of the leaf . C 4 plants can produce more sugar than C 3 plants in conditions of high light and temperature . Many important crop plants are C 4 plants, including maize , sorghum , sugarcane , and millet . Plants that do not use PEP-carboxylase in carbon fixation are called C 3 plants because the primary carboxylation reaction , catalyzed by RuBisCO, produces

3913-462: The photosystems , quantum efficiency and the CO 2 assimilation rates. With some instruments, even wavelength dependency of the photosynthetic efficiency can be analyzed . A phenomenon known as quantum walk increases the efficiency of the energy transport of light significantly. In the photosynthetic cell of an alga , bacterium , or plant, there are light-sensitive molecules called chromophores arranged in an antenna-shaped structure called

4004-437: The plasma membrane . In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by the splitting of water is used in the creation of two important molecules that participate in energetic processes: reduced nicotinamide adenine dinucleotide phosphate (NADPH) and ATP. In plants, algae, and cyanobacteria, sugars are synthesized by

4095-450: The reverse Krebs cycle are used to achieve the same end. The first photosynthetic organisms probably evolved early in the evolutionary history of life using reducing agents such as hydrogen or hydrogen sulfide, rather than water, as sources of electrons. Cyanobacteria appeared later; the excess oxygen they produced contributed directly to the oxygenation of the Earth , which rendered

4186-410: The APG below). A classification presents a view at a particular point in time, based on a particular state of research. Independent researchers, including members of the APG, continue to publish their own views on areas of angiosperm taxonomy. Classifications change, however inconvenient this is to users. However, the APG publications are increasingly regarded as an authoritative point of reference and

4277-516: The Asparagaceae or as separate families. Some of the main changes in APG II were: In 2007, a paper was published giving a linear ordering of the families in APG II, suitable for ordering herbarium specimens, for example. The third paper from the APG updates the system described in the 2003 paper. The broad outline of the system remains unchanged, but the number of previously unplaced families and genera

4368-433: The CO 2 concentration in the leaves under these conditions. Plants that use the C 4 carbon fixation process chemically fix carbon dioxide in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalyzed by an enzyme called PEP carboxylase , creating the four-carbon organic acid oxaloacetic acid . Oxaloacetic acid or malate synthesized by this process

4459-419: The action spectrum is blue-green light, which allows these algae to use the blue end of the spectrum to grow in the deeper waters that filter out the longer wavelengths (red light) used by above-ground green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria ) and is the least effective for photosynthesis in

4550-449: The arrangement of their collections to match the latest APG system. In the past, classification systems were typically produced by an individual botanist or by a small group. The result was a large number of systems (see List of systems of plant taxonomy ). Different systems and their updates were generally favoured in different countries. Examples are the Engler system in continental Europe,

4641-521: The atmosphere. Although there are some differences between oxygenic photosynthesis in plants , algae , and cyanobacteria , the overall process is quite similar in these organisms. There are also many varieties of anoxygenic photosynthesis , used mostly by bacteria, which consume carbon dioxide but do not release oxygen. Carbon dioxide is converted into sugars in a process called carbon fixation ; photosynthesis captures energy from sunlight to convert carbon dioxide into carbohydrates . Carbon fixation

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4732-426: The basis of genetic characteristics. The paper explained the authors' view that there is a need for a classification system for angiosperms at the level of families, orders and above, but that existing classifications were "outdated". The main reason why existing systems were rejected was because they were not phylogenetic , i.e. not based on strictly monophyletic groups (groups which consist of all descendants of

4823-402: The broader asparagus family ( Asparagaceae ). The authors say that alternative circumscriptions, as in APG I and II, are likely to cause confusion and that major herbaria which are re-arranging their collections in accordance with the APG approach have all agreed to use the more inclusive families. This approach is being increasingly used in collections in herbaria and botanic gardens . In

4914-480: The carboxysome quickly sponges it up. HCO 3 ions are made from CO 2 outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein. They cannot cross the membrane as they are charged, and within the cytosol they turn back into CO 2 very slowly without the help of carbonic anhydrase. This causes the HCO 3 ions to accumulate within the cell from where they diffuse into

5005-491: The carboxysomes. Pyrenoids in algae and hornworts also act to concentrate CO 2 around RuBisCO. The overall process of photosynthesis takes place in four stages: Plants usually convert light into chemical energy with a photosynthetic efficiency of 3–6%. Absorbed light that is unconverted is dissipated primarily as heat , with a small fraction (1–2%) reemitted as chlorophyll fluorescence at longer (redder) wavelengths . This fact allows measurement of

5096-439: The casings of pollen grains have horizontally extended thin regions (or endo-apertures ). The gynoecium is placed on a short stalk, papillae on the stigma consist of two or more cells, ovary locules taper upwards, and the protective cell layer (or integument ) surrounding the ovule leaves a zigzag opening (or micropyle ). Some cell clusters have bundles of long yellow crystals, mucilage cells are present, and seeds have

5187-454: The classification [...] will not need much further change." A major change is that the paper discontinues the use of 'bracketed' families in favour of larger, more inclusive families. As a result, the APG III system contains only 415 families, rather than the 457 of APG II. For example, the agave family ( Agavaceae ) and the hyacinth family ( Hyacinthaceae ) are no longer regarded as distinct from

5278-409: The conditions of non-cyclic electron flow in green plants is: Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants , the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with absorption peaks in violet-blue and red light. In red algae ,

5369-503: The diagram), a chemiosmotic potential is generated by pumping proton cations ( H ) across the membrane and into the thylakoid space . An ATP synthase enzyme uses that chemiosmotic potential to make ATP during photophosphorylation , whereas NADPH is a product of the terminal redox reaction in the Z-scheme . The electron enters a chlorophyll molecule in Photosystem I . There it

5460-505: The equation for this process is: This equation emphasizes that water is both a reactant in the light-dependent reaction and a product of the light-independent reaction , but canceling n water molecules from each side gives the net equation: Other processes substitute other compounds (such as arsenite ) for water in the electron-supply role; for example some microbes use sunlight to oxidize arsenite to arsenate : The equation for this reaction is: Photosynthesis occurs in two stages. In

5551-518: The evolution of complex life possible. The average rate of energy captured by global photosynthesis is approximately 130 terawatts , which is about eight times the total power consumption of human civilization . Photosynthetic organisms also convert around 100–115 billion tons (91–104 Pg petagrams , or billions of metric tons), of carbon into biomass per year. Photosynthesis was discovered in 1779 by Jan Ingenhousz . He showed that plants need light, not just air, soil, and water. Photosynthesis

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5642-400: The family level. The second paper published by the APG in 2003 presented an update to the original classification of 1998. The authors stated that changes were proposed only when there was "substantial new evidence" which supported them. The classification continued the tradition of seeking broad circumscriptions of taxa, for example trying to place small families containing only one genus in

5733-408: The family name Asphodelaceae is used instead of Xanthorrhoeaceae , and Francoaceae is used instead of Melianthaceae (and now also includes Vivianiaceae ). This brings the total number of orders and families recognized in the APG system to 64 and 416, respectively. Two additional informal major clades, superrosids and superasterids , that each comprise the additional orders that are included in

5824-582: The first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the hydrogen carrier NADPH and the energy-storage molecule ATP . During the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide. Most organisms that use oxygenic photosynthesis use visible light for the light-dependent reactions, although at least three use shortwave infrared or, more specifically, far-red radiation. Some organisms employ even more radical variants of photosynthesis. Some archaea use

5915-441: The first step of the Z-scheme , requires an external source of electrons to reduce its oxidized chlorophyll a reaction center. The source of electrons for photosynthesis in green plants and cyanobacteria is water. Two water molecules are oxidized by the energy of four successive charge-separation reactions of photosystem II to yield a molecule of diatomic oxygen and four hydrogen ions. The electrons yielded are transferred to

6006-464: The following are some examples of the influence of the APG system: The principles of the APG's approach to classification were set out in the first paper of 1998, and have remained unchanged in subsequent revisions. Briefly, these are: For a detailed discussion on phylogenetic nomenclature, see Cantino et al. (2007). ) The initial 1998 paper by the APG made angiosperms the first large group of organisms to be systematically re-classified primarily on

6097-399: The interior of a cell, giving the membrane a very large surface area and therefore increasing the amount of light that the bacteria can absorb. In plants and algae, photosynthesis takes place in organelles called chloroplasts . A typical plant cell contains about 10 to 100 chloroplasts. The chloroplast is enclosed by a membrane. This membrane is composed of a phospholipid inner membrane,

6188-433: The interior tissues of a leaf, called the mesophyll , can contain between 450,000 and 800,000 chloroplasts for every square millimeter of leaf. The surface of the leaf is coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to minimize heating . The transparent epidermis layer allows light to pass through to

6279-617: The larger clades dominated by the rosids and asterids are also included. APG IV also uses the linear approach (LAPG) as advocated by Haston et al. (2009) In a supplemental file Byng et al. provide an alphabetical list of families by orders. Peter Stevens , one of the authors of all four of the APG papers, maintains a web site, the Angiosperm Phylogeny Website (APWeb), hosted by the Missouri Botanical Garden , which has been regularly updated since 2001, and

6370-434: The light reaction, and infrared gas analyzers can measure the dark reaction . An integrated chlorophyll fluorometer and gas exchange system can investigate both light and dark reactions when researchers use the two separate systems together. Infrared gas analyzers and some moisture sensors are sensitive enough to measure the photosynthetic assimilation of CO 2 and of Δ H 2 O using reliable methods . CO 2

6461-433: The light-independent reaction); at that point, the path of that electron ends. The cyclic reaction is similar to that of the non-cyclic but differs in that it generates only ATP, and no reduced NADP (NADPH) is created. The cyclic reaction takes place only at photosystem I. Once the electron is displaced from the photosystem, the electron is passed down the electron acceptor molecules and returns to photosystem I, from where it

6552-432: The more common types of photosynthesis. In photosynthetic bacteria, the proteins that gather light for photosynthesis are embedded in cell membranes . In its simplest form, this involves the membrane surrounding the cell itself. However, the membrane may be tightly folded into cylindrical sheets called thylakoids , or bunched up into round vesicles called intracytoplasmic membranes . These structures can fill most of

6643-439: The most efficient route, where it will have the highest probability of arriving at its destination in the minimum possible time. Because that quantum walking takes place at temperatures far higher than quantum phenomena usually occur, it is only possible over very short distances. Obstacles in the form of destructive interference cause the particle to lose its wave properties for an instant before it regains them once again after it

6734-459: The naming of higher orders. Such a consensus proved relatively easy to achieve but the resultant tree was highly unresolved. That is, while the relationship of orders was established, their composition was not. Other features of the proposed classification included: A major outcome of the classification was the disappearance of the traditional division of the flowering plants into two groups, monocots and dicots . The monocots were recognized as

6825-574: The ordinal level. In the development of a fourth version there was some controversy over the methodology, and the development of a consensus proved more difficult than in previous iterations. In particular Peter Stevens questioned the validity of discussions regarding family delimitation in the absence of changes of phylogenetic relationships. Further progress was made by the use of large banks of genes, including those of plastid , mitochondrial and nuclear ribosomal origin, such as that of Douglas Soltis and colleagues (2011). The fourth version

6916-498: The organic compounds through cellular respiration . Photosynthesis plays a critical role in producing and maintaining the oxygen content of the Earth's atmosphere, and it supplies most of the biological energy necessary for complex life on Earth. Some bacteria also perform anoxygenic photosynthesis , which uses bacteriochlorophyll to split hydrogen sulfide as a reductant instead of water, producing sulfur instead of oxygen. Archaea such as Halobacterium also perform

7007-410: The organism's metabolism . Photosynthesis and cellular respiration are distinct processes, as they take place through different sequences of chemical reactions and in different cellular compartments (cellular respiration in mitochondria ). The general equation for photosynthesis as first proposed by Cornelis van Niel is: Since water is used as the electron donor in oxygenic photosynthesis,

7098-556: The photosynthetic system. Plants absorb light primarily using the pigment chlorophyll . The green part of the light spectrum is not absorbed but is reflected, which is the reason that most plants have a green color. Besides chlorophyll, plants also use pigments such as carotenes and xanthophylls . Algae also use chlorophyll, but various other pigments are present, such as phycocyanin , carotenes , and xanthophylls in green algae , phycoerythrin in red algae (rhodophytes) and fucoxanthin in brown algae and diatoms resulting in

7189-476: The production of amino acids and lipids . In hot and dry conditions , plants close their stomata to prevent water loss. Under these conditions, CO 2 will decrease and oxygen gas , produced by the light reactions of photosynthesis, will increase, causing an increase of photorespiration by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and decrease in carbon fixation. Some plants have evolved mechanisms to increase

7280-486: The relationship between the two can be complex. For example, the light reaction creates ATP and NADPH energy molecules , which C 3 plants can use for carbon fixation or photorespiration . Electrons may also flow to other electron sinks. For this reason, it is not uncommon for authors to differentiate between work done under non-photorespiratory conditions and under photorespiratory conditions . Chlorophyll fluorescence of photosystem II can measure

7371-462: The respective organisms . In plants , light-dependent reactions occur in the thylakoid membranes of the chloroplasts where they drive the synthesis of ATP and NADPH . The light-dependent reactions are of two forms: cyclic and non-cyclic . In the non-cyclic reaction, the photons are captured in the light-harvesting antenna complexes of photosystem II by chlorophyll and other accessory pigments (see diagram at right). The absorption of

7462-414: The same volume of the journal, two related papers were published. One gives a linear ordering of the families in APG III; as with the linear ordering published for APG II, this is intended for ordering herbarium specimens, for example. The other paper gives, for the first time, a classification of the families in APG III which uses formal taxonomic ranks ; previously only informal clade names were used above

7553-479: The site of carboxylation in the chloroplast, to replace Ci. CO 2 concentration in the chloroplast becomes possible to estimate with the measurement of mesophyll conductance or g m using an integrated system. Photosynthesis measurement systems are not designed to directly measure the amount of light the leaf absorbs, but analysis of chlorophyll fluorescence , P700 - and P515-absorbance, and gas exchange measurements reveal detailed information about, e.g.,

7644-461: The three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle . Over 90% of plants use C 3 carbon fixation, compared to 3% that use C 4 carbon fixation; however, the evolution of C 4 in over sixty plant lineages makes it a striking example of convergent evolution . C 2 photosynthesis , which involves carbon-concentration by selective breakdown of photorespiratory glycine,

7735-424: The ultimate reduction of NADP to NADPH . In addition, this creates a proton gradient (energy gradient) across the chloroplast membrane , which is used by ATP synthase in the synthesis of ATP . The chlorophyll molecule ultimately regains the electron it lost when a water molecule is split in a process called photolysis , which releases oxygen . The overall equation for the light-dependent reactions under

7826-408: The water-oxidizing reaction (Kok's S-state diagrams). The hydrogen ions are released in the thylakoid lumen and therefore contribute to the transmembrane chemiosmotic potential that leads to ATP synthesis . Oxygen is a waste product of light-dependent reactions, but the majority of organisms on Earth use oxygen and its energy for cellular respiration , including photosynthetic organisms . In

7917-404: Was "rudely shattered". This posed problems for all users of classification systems (including encyclopaedists). The impetus came from a major molecular study published in 1993 based on 5000 flowering plants and a photosynthesis gene ( rbcL ). This produced a number of surprising results in terms of the relationships between groupings of plants, for instance the dicotyledons were not supported as

8008-454: Was based on their morphology (particularly of their flower) and biochemistry (the kinds of chemical compounds in the plant). After the 1980s, detailed genetic evidence analysed by phylogenetic methods became available and while confirming or clarifying some relationships in existing classification systems, it radically changed others. This genetic evidence created a rapid increase in knowledge that led to many proposed changes; stability

8099-462: Was emitted, hence the name cyclic reaction . Linear electron transport through a photosystem will leave the reaction center of that photosystem oxidized . Elevating another electron will first require re-reduction of the reaction center. The excited electrons lost from the reaction center ( P700 ) of photosystem I are replaced by transfer from plastocyanin , whose electrons come from electron transport through photosystem II . Photosystem II, as

8190-904: Was finally published in 2016. It arose from an international conference hosted at the Royal Botanical Gardens in September 2015 and also an online survey of botanists and other users. The broad outline of the system remains unchanged but several new orders are included ( Boraginales , Dilleniales , Icacinales , Metteniusales and Vahliales ), some new families are recognised ( Kewaceae , Macarthuriaceae , Maundiaceae , Mazaceae , Microteaceae , Nyssaceae , Peraceae , Petenaeaceae and Petiveriaceae ) and some previously recognised families are lumped ( Aristolochiaceae now includes Lactoridaceae and Hydnoraceae ; Restionaceae now re-includes Anarthriaceae and Centrolepidaceae ; and Buxaceae now includes Haptanthaceae ). Due to nomenclatural issues,

8281-439: Was in 1998, and attracted considerable media attention. The intention was to provide a widely accepted and more stable point of reference for angiosperm classification. As of 2016 , three revisions have been published, in 2003 (APG II), in 2009 (APG III) and in 2016 (APG IV), each superseding the previous system. Thirteen researchers have been listed as authors to the three papers, and a further 43 as contributors (see Members of

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